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Effects of Eggshell Pigmentation and Egg Size on the Spectral Properties and Characteristics of Eggshell of Meat and Layer Breeder Eggs
T. M. Shafey*, T. H. Al-mohsen, A. A. Al-sobayel, M. J. Al-hassan and M. M. Ghnnam1 Department of Animal Production, University of King Saud, College of Agriculture P.O. Box 2460, Riyadh 11451, Saudi Arabia
ABSTRACT : The effects of eggshell pigmentation and egg size (medium and large) on the spectral properties and characteristics of eggshells were examined in eggs from two genetic groups of breeder flocks. Birds from meat (Hybro, pigmented eggshell, PES) and layer (Leghorn, non-pigmented eggshell, NPES) at 40 and 46 weeks of age, respectively, were used. Measurements of per cent shell (PS), shell thickness (ST), shell volume (SV), shell density (SD), egg shell conductance (EC) and physical dimensions of eggs were made. The spectral properties of eggshells were measured over the wavelength (WL) range of 200 to 1,100 nm. Eggshell absorbed approximately 99.8 percent of the light and transmitted only about 0.12 percent with a maximum light transmission at the near-infra-red region of about 1075 nm. It attenuated shorter WL and transmitted longer WL. Eggshell pigmentation and egg size influenced light transmission into the egg. The NPES had higher EC and transmission of light and lower PS and SD than those of the PES. Large size eggs had higher EC, SD, SV, transmission of light and egg physical dimensions than those of medium size eggs. It is concluded that genetic make up of birds and egg size influenced eggshell characteristics including EC and that, as a consequence, the difference in the spectral properties of eggshells. The pigmentation of eggshell influenced the amount and WL transmitted into the egg. The size and EC of eggs influenced the amount of light transmitted through the eggshell. EC is a good indicator for the ability of eggshell to transmit light. (Asian-Aust. J. Anim. Sci. 2002. Vol 15, No. 2 : 297-302)
Key Words : Egg Size, Shell Characteristics, Shell Pigmentation, Spectral Characteristics, Breeder Flocks
INTRODUCTION to reflect, absorb and transmit light. These include shell pigmentation, thickness, density and conductance. Several Investigations on the effects of illumination of factors such as egg size and genetic make up of birds are incubated chickens’eggs upon embryonic growth and known to influence eggshell characteristics (Marshall and hatchability have been inconsistent. The growth rate of Cruickshank, 1938; Christensen and Nestor, 1994; chick embryo increases (Garwood et al., 1973; Lowe and Christensen et al., 1995) and consequently could influence Garwood, 1977), hatching period decreases (Shutze et al., the spectral characteristics of eggshells and the outcome of 1962; Lauber and Shutze, 1964; Siegel et al., 1969; Walter incubated eggs under light. The objectives of this study and Voitle, 1972); and hatchability percentage improves were to assess the effects of eggshell pigmentation and egg (Shutze et al., 1962; Gimeno et al., 1967; Walter and Voitle, size on the characteristics of eggshell including spectral 1972) indicating a beneficial role for incubating eggs under properties, and physical dimensions of eggs from two light. In contrast, Lauber and Shutze (1964), Siegel et al. genetic groups of birds. A commercial meat-type (Hybro, (1969) and Zakaria (1989) found no effect on hatchability brown eggshell, pigmented eggshell, PES) and a layer-type when eggs were exposed to light during incubation period. (Leghorn, white eggshell, non-pigmented eggshell, NPES) Whilst, Tamimie (1967) and Tamimie and Fox (1967) breeder flocks were used. reported a delay in hatching time, reduced hatchability and increased incidence of embryonic abnormalities in those MATERIALS AND METHODS chicks exposed to light during incubation. This disagreement among authors suggests that there are some A total of 56 freshly laid eggs obtained from a factors influencing the quantity and quality of light that commercial meat-type (Hybro, brown eggshell, pigmented reaches the embryos and consequently the outcome of eggshell, PES) and a layer (Leghorn, white eggshell, non- incubated eggs under light. pigmented eggshell, NPES, King Saud University flock) The characteristics of eggshell may influence its ability breeders at 40 and 46 weeks of age, respectively, were used in this study. Birds were fed a standard breeder ration (16% * Address reprint request to T. M. Shafey, Tel: +966-1-4678785, CP, 12 MJ of ME per kg, 3.4% calcium, 0.45% available Fax: +966-1-4678474, E-mail: [email protected] phosphorus) and reared under standard husbandry 1 Department of Physics, University of King Saud, College of conditions. A photoperiod of 14 h commenced when the Science, PO. Box 2455, Riyadh 11451, Saudi Arabia. Received June 5, 2001; Accepted August 21, 2001 birds were caged at 22 weeks of age and was maintained
298 SHAFEY ET AL. throughout the trials. Eggs were weighed individually and once a day to determine the EC, expressed as the milligrams graded into two weight classes. Leghorn’s eggs weighing of water lost per day per Torr. Weight loss was corrected to between 58 and 64 g, and 64.1 and 70 g were considered a standard barometric pressure of 760 Torr (mm Hg) (Ar et medium and large sizes, respectively. Hybro’s eggs al., 1974). EC was also expressed per unit of egg weight weighing between 55 and 60 g, and 60.1 and 70 g were (EC/EW) to adjust for the effect of egg weight on EC. considered medium and large sizes, respectively. Shell volume was calculated from the relationship: Volume = A × L; where A=surface area of the egg (cm2), and Eggshell characteristics and spectral properties L=thickness of the shell (cm). Surface area of the egg was Seven eggs selected at random from each weight class estimated from the allometric relationship, area (cm2) = from both genetic groups were weighed individually and 4.835 W 0.662 where W = initial egg weight (Paganelli et al., broken open. Eggshells were washed with water, dried with 1974). paper towels and then weighed. Eggshells were broken to Measurements included egg weight, egg length, egg obtain representative areas. Pieces from the three different width, PS, ST, egg surface area, shell volume, shell density, areas (large end, equator and small end) of each shell were EC and spectral absorption of eggshell over the WL range selected. Twelve measurements were taken from each of 200 to 1,100 nm. eggshell with a micrometer (Ames, Waltham, MA). Data collected were subjected to analysis of variance Measurements of shell weight (SW), per cent shell (SAS Institute, 1985). When significant variance ratios (PS)=SW/egg weight×100 and eggshell thickness (ST) were were detected, differences between treatment means were done with the membranes intact. Four eggshells from each tested using the least significant difference (LSD) weight classes from both genetic groups were selected and procedures. membranes were removed then spectral absorption of RESULTS eggshells were determined using a spectrophotometer (Model UV-1601 PC). Eggshell spectral absorption was The physical dimensions, eggshell characteristics and recorded every 2 nm over the wavelength (WL) range of EC of medium and large sizes of eggs from the PES and 200 to 1,100 nm. Calculations were based on 25 nm-groups NPES (Hybro and Leghorn birds, respectively) groups are for WL absorption. shown in tables 1 and 2, respectively. Eggs produced by Hybro had higher weight, length, PS and shell volume and Eggshell conductance (EC) lower EC (expressed as mg day-1 torr-1 or mg day-1 torr-1 Seven freshly laid eggs from each weight class from per 100 g egg weight (EC/EW)) than those produced by both genetic group were selected at random, individually Leghorn birds. The physical dimensions (weight, length, weighed, placed in desiccators containing fresh desiccant width and surface area), eggshell thickness and volume and -1 -1 (CaSO4, Sigma Chemical Co., St. Louis, USA) and EC (expressed as mg day torr ) of large size eggs were maintained at 25°C for 4 days. These eggs were weighed higher than those of medium size eggs. There were no
Table 1. Physical dimensions and eggshell characteristics of medium and large sizes of eggs from two genetic groups of birds (meat (Hybro, pigmented eggshell) and layer (Leghorn, non-pigmented eggshell) breeders) Physical dimensions of eggs Egg shell characteristics Surface Treatment Weight Length Width Thickness Vo lu me Density area Per cent1 (g) (cm) (cm) (mm) (cm3) (g/cm3) (cm3) Genetic group (GG) Hybro 63.5 5.9 4.37 75.5 9.7 0.39 2.97 2.08 Leghorn 62.0* 5.7** 4.44 74.4 9.2** 0.38 2.81* 2.03 Egg size (ES) Medium 59.0 5.7 4.31 71.9 9.4 0.37 2.69 2.06 Large 66.4** 5.9* 4.49** 77.8** 9.5 0.40* 3.09** 2.06 SEM2 0.5 0.1 0.02 0.6 0.1 0.01 0.05 0.02 Probability (P) GG 0.0479 0.0006 0.0582 0.2051 0.0046 0.0832 0.0404 0.1966 ES 0.0001 0.0176 0.0001 0.0001 0.3219 0.0221 0.0001 0.9835 GG × ES 0.7011 0.3600 0.0690 0.7130 0.1004 0.1614 0.2821 0.4113 1 As a percentage of egg weight, 2 Standard error of means. * Significant difference (p<0.05), ** Significant difference (p<0.01).
SPECTRAL PROPERTIES AND CHARACTERISTICS OF EGGSHELL 299 differences between the two genetic groups of birds in egg Spectral absorption of eggshells of medium and large width, egg surface area and shell thickness and density. sizes of eggs from the PES (Hybro) and NPES (Leghorn) No significant differences were detected between the groups are shown in table 3. The PES group had medium and large sizes of eggs in PS, shell density and significantly (p<0.01) higher absorption and lower EC/EW. transmission percentages of light over the WL range measured (200 to 1,100 nm) than those of the NPES group. There was a significant interaction (p<0.01) between eggshell pigmentation and egg size on the spectral Table 2. Egg weight and eggshell conductance (EC) of absorption of eggshell over the WL range measured medium and large sizes of eggs from two genetic groups of (table 4). Eggshells of medium size eggs of the NPES group birds (meat (Hybro, pigmented eggshell) and layer had a higher percentage of spectral absorption over the WL (Leghorn, non-pigmented eggshell) breeders) range measured than those of large size eggs of the same Egg EC EC/100 g genetic group. Whilst, the percentage of spectral absorption Treatment weight (mg day-1 torr-1) egg weight of eggshells over the WL range between 200 and 470 nm (g) was not influenced by egg size in the PES group. Eggshells Genetic group of medium size eggs of the PES group had a higher (GG) percentage of spectral absorption over the WL range of 470 Hybro 61.9 10.83 17.49 to 1,100 nm than those of large size eggs of the PES group Leghorn 60.8** 11.78* 19.36* and both sizes of eggs in the NPES group. Egg size (ES) Medium 59.8 10.85 18.14 DISCUSSION
Large 62.9** 11.75* 18.71 Results from the spectral absorption of PES and NPES SEM1 0.2 0.3 0.5 of eggs (tables 3 and 4) revealed that eggshell absorbed Probability (P) approximately 99.8 percent of the light and exhibited GG 0.0003 0.0451 0.0163 approximately 0.12 percent transmission (Transmission ES 0.0001 0.0498 0.4334 percent=100-absorption percent) with a maximum light GG × ES 0.2402 0.7547 0.4694 transmittance at the near-infra red (near-IR) region of about 1 Standard error of means. 1075 nm (figures 1 and 2). Whilst eggshell absorbed light * Significant difference (p<0.05). maximally in the near-ultra violet (near-UV) range from ** Significant difference (p<0.01). 200-300 nm. Eggshell absorption reduced the ability of light to reach the embryo. Eggshell attenuated shorter WL
Table 3. The main effects of eggshell pigmentation and egg size on the spectral absorption percentage of eggshell over the wave length (WL) range of 200 to 1,100 nm WL< =380 380 300 SHAFEY ET AL. Table 4. The combined effects of eggshell pigmentation major role in controlling the WL transmitted through the and egg size on the spectral absorption percentage of eggshell. The non-significant difference in spectral eggshell over the wave length (WL) range of 200 to absorption of eggshells between medium and large eggs in 1,100 nm the PES group over the WL range 200 to 470 nm when Genetic group compared with their counterparts of the NPES group Wave length Hybro (PES) Leghorn (NPES) suggest a strong ability for eggshell pigmentation to absorb (WL) SEM1 Egg size Egg size these WL, regardless to egg size. Consequently, the amount (nm) Medium Large Medium Large of pigment present in the eggshell may alter the spectral WL< =380 99.960a 99.955a 99.957a 99.947b 0.002 absorption. In addition, there is a considerable variation in 380 SPECTRAL PROPERTIES AND CHARACTERISTICS OF EGGSHELL 301 99.99 Transmitted Pigmented eggshell (Hybro) 99.96 Non-pigmented eggshell (Leghorn) 99.93 99.9 99.87 Absorption percentage 99.84 Absorbed 99.81 1234567891011121314151617181920212223242526272829303132333435 Wavelength (WL, nm) 1=WL<=250, 2=250 Figure 1. Spectral absorption percentage of pigmented and non-pigmented eggshells of eggs obtained from two genetic groups of birds (meat (Hybro) and layer (Leghorn) breeders 100 Transmitted Medium size eggs 99.95 Large size eggs 99.9 99.85 Absorbed Absorption percentage 99.8 99.75 1 2 3 4 5 6 7 8 9 1011121314151617181920212223242526272829303132333435 Wave lenght (WL, nm) 1=WL<=250, 2=250 Figure 2. Spectral absorption percentage of eggshells obtained from medium and large sizes of eggs influenced the amount and WL transmitted into the egg. transmitted through the eggshell. 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